1. Field of the Invention
The present invention relates to an image reading apparatus for photo-electrically reading an original image and, more particularly, to an image reading apparatus capable of reading an image of either a sheet original or a cubic original (book original) such as a book.
2. Description of the Related Art
A facsimile apparatus is known as an apparatus for photo-electrically reading an original image, electrically processing an image signal obtained by reading, and transmitting or recording the processed signal.
In such a facsimile apparatus, a sheet original such as a document or drawing is often processed. Therefore, in order to simplify a mechanical arrangement and to reduce the size of the apparatus, an image reading mechanism is generally arranged such that a sheet original is carried by rollers or the like and an image of the sheet original carried through a reading position is read by a line sensor such as a CCD.
It is, however, sometimes necessary to facsimile-transmit not only a sheet original but also an original (to be referred to as a book original hereinafter) having a thickness such as a book. In such a case, an operation must be performed in an order such that a book original is copied into the form of a sheet original and then subjected to a read operation by the reading unit of the facsimile apparatus.
When a large number of pages of a book are to be facsimile-transmitted, therefore, a large number of copies must be prepared, resulting in a cost- and time-consuming operation.
For this reason, an apparatus in which a book original can be read by a reading apparatus for a sheet original is proposed. That is, a sheet urging unit for sandwiching and carrying a sheet original is opened, and a book original having a thickness is moved on the sheet urging unit.
With this arrangement, since both sheet and book originals can be facsimile-transmitted by a single facsimile apparatus, time and cost problems can be solved.
In such an image photo-electrical reading apparatus, nonuniformity correction processing called shading correction is performed for an image signal. In order to perform this correction operation, a white reference plate arranged at a sheet original reading unit is read to measure a shading distortion.
When the sheet urging unit for a sheet original is opened in order to read not only a sheet original but also a book original, however, reading of the white reference plate cannot be performed. Therefore, measurement of the shading distortion for shading correction cannot be performed upon reading of a book original.
In addition, upon reading of a book original, an original end is read as black information and output as an unnecessary black signal. This reduces, e.g., a compression efficiency or storage efficiency.